Packaging film



N. R. PETERSON PACKAGING FILM Aug- 18, 1970 Filed July 1. 1965 INVENTOR.Norman 1?. Pewerson QGEN T United States Patent ()flice 3,524,795PACKAGING FILM Norman R. Peterson, Midland, Mich., assignor to The DowChemical Company, Midland, Mich., a corporation of Delaware Filed July1, 1965, Ser. No. 468,886 Int. Cl. B32b 7/02, 31/30; B65b 25/00 U.S. Cl.161-165 11 Claims ABSTRACT OF THE DISCLOSURE Layered barrier packagingfilms are disclosed which employ polyolefin outer layers and gas barrierinner layers. The films thermoform well and are eminently suited forfood packaging and the like.

This invention relates to an improved packaging film and moreparticularly relates to a composite mnlti-layer packaging film.

The application of synthetic, resinous, flexible, thermoplastic films inthe packaging art has become widespread. However, for many packagingapplications, the known synthetic resinous films are not entirelysatisfactory. It is possible to prepare packaging films having a widevariety of characteristics and any single desirable characteristic whichis possessed by a synthetic, resinous, thermoplastic composition isusually readily attained. However, to obtain a useful packaging film, itmust have many and varied properties. For desirable commercialapplication, such as in the area of the packaging of cheese andprocessed meats, much more is required from a packaging film than themere fact that it is transparent and scalable by one means or the other.For an optimum film which provides product protection and desirableprocessability, it must be a reasonable barrier to the passage ofoxygen, carbon dioxide, and moisture vapor. Oxygen passing through apackaging film of cheese or processed meat frequently results inspoilage. Similarly, the undesired loss of carbon dioxide can causeunfavorable alteration in color in the keeping properties of a packagedmeat or cheese. The film should be relatively resistant to the passageof moisture vapor, otherwise the cheese or meat product will dry andbecome unsightly.

Oftentimes in the packaging of processed meat and cheese for consumerconsumption, the packages are prepared under not too carefullycontrolled conditions and oftentimes such packaging is done at theretail outlet where control of the sealing of the package to an optimumdegree is not easily achieved. Therefore, a desirable packaging film forprocessed meat and cheese must be heat sealable and heat sealable over arelatively wide range of temperatures without causing unsightlydeformation of the resultant package.

Oftentimes sliced processed meats are packaged between two preformedportions of film which are vacuum or pressure formed to a contourclosely approximating that of the final desired article to be packaged.For example, oftentimes a rectangular meat loaf is sliced into aplurality of slices and is packaged in portions of one-half or one poundand, in order to provide an attractive package, at least one portion ofthe film is pressure formed or is vacuum formed in a mold to form arectangular container 3,524,795 Patented Aug. 18, 1970 closelyconforming to the configuration of the quantity of meat. Many filmshaving desirable packaging characteristics do not pressure form over awide range of temperatures and indeed some form poorly even in anoptimum narrow range of temperatures. It is essential and critical inthe formation of such a package that the film draw or form in such amanner that all portions of the package have a relatively uniformthickness. For example, it is not unusual in forming a 2 mil thick filminto a shallow rectangular container 4 inches by 4 inches and an inchand a half deep to discover that the thickness of the formed containerin the corners where three sides meet is somewhere in the range of aquarter to one-half mil.

Oftentimes a film having poor thermoforming characteristics will ruptureand not provide a useful product. In order to provide a satisfactorypackaging film, it is necessary that such thermoforming is accomplishedin a relatively simple and economical manner. Further, a desirablepackaging film must be relatively abrasion resistant. It must not scaror scratch when abraded by like or different materials under conditionsof food handling and transportation. Abrasion of the film in theresultant package is highly undesirable as it frequently results infailure of the package by rupture or by causing the package to becomeunsightly and therefore not attractive to the purchaser. A film which issuitable for the wrapping of processed meat products and cheese mostdesirably should be a limp film, that is, a film that readily conformsto the shape of the product being packaged and is not stiff or noisy.Such a limp film might well be termed as a soft film as distinguishedfrom hard films, such as polystyrene and the like. Often, processedmeats and cheeses are packaged in such a manner that the plane surfaceof the film does not readily conform to the configuration of thepackage, that is, the article to be packaged does not have cubic orrectangular configuration. Thus, a sheet of film must wrinkle and beresistant to failure under such wrinkling, that is, the film must becrumple resistant. It must maintain its barrier properties after beingcrumpled or wrinkled in order to provide a successful and usefulpackage. The ideal packaging film for cheeses and processed meatsideally has a low shrink energy, that is, on being heated to itsthermoplastic temperature, it has relatively low shrink energy. The lowtendency to shrink is of great benefit when thermoforming, as theclamping pressures are low, and high precision clamps requiring a greatdeal of maintenance are not needed in the thermoforming apparatus. It isparticularly essential and critical for a packaging film to have a highgloss and clarity. If the film does not have a high gloss and is notclear, the resultant package is unattractive to the buyer and the filmis therefore unsatisfactory. Printability is an extremely desirablecharacteristic to have in a packaging film for processed meat and cheesewherein various indicia may be readily printed upon the surfacetherefore by conventional processes. Another characteristic which isvery desirable in a packaging film for cheese and processed meats isthat of having a relatively high strength at the sealing temperature.For example, a film of a polymer which has a sharp crystalline meltingpoint is undesirable in many applications as heating the film to atemperature sufiiciently high to result in heat sealing of the film toitself or to another material requires extremely close control ofsealing temperatures and of manipulation of the package during thesealing operation. For example, polyvinylidene chloride copolymerscontaining major portions of polymerized vinylidene chloride are usuallyextremely ditficult to heat seal as the temperature must be closelycontrolled and such films at the heat sealing temperature become quitefluid and exhibit little or no strength. A film having high strength atheat sealing temperatures is extremely desirable as the sealingconditions may be varied to a much greater extent and yet result in anacceptable package. For example, with a film of low heat seal strength,sealing may be accomplished under ideal conditions but premature removalof the package by the operator may result in unsightly deformation ofthe film and result in loss of the package and the necessity ofrepackaging the contents. Thus, it is highly desirable at heat sealingtemperatures that the film exhibit relatively high mechanical strength.Individually, such characteristics are easily obtainable with knownpackaging films. However, the combination of these characteristics intoa single packaging film is not known.

The present invention provides a packaging film having the foregoingunique combination of beneficial and advantageous properties and thesefeatures and advantages are obtained in a flexible packaging filmcomprising at least one inner or central layer having first and secondmajor surfaces and first and second outer layers adhered to the majorsurfaces of the central layer, the central layer being generally anunoriented barrier material, the surface layers comprising a generallyunoriented polyolefin.

By the term polyolefin" is meant polyethylene, polypropylene resinouscopolymers of ethylene and propylene, copolymers of ethylene and/orpropylene with minor proportions of olefinically unsaturated monomerssuch as, for example, those alpha-olefins having from 2 to 8 carbonatoms such as l-butene, l-pentene, l-hexene, l-heptene, l-octene andmixed higher alphaolefins. Other hydrocarbons useful for makingcopolymers with ethylene and propylene include divinylbenzene, allene,dimethallyl, and isopentene. Comonomers which can broadly be usedinclude mono-substituted ethylenes such as l-pentene, vinylcyclohexene,allyl benzene, C -C mixed alphaolefins, styrene, allyl naphthalene, andthe like, 1,1-disubstituted ethylenes such as alphamethyl styrene, 2-methylbutene-l, mixed alphaand beta-pinenes, camphene and the like, 1,2disubstituted ethylenes such as indene, acenaphthylene, cyclopentene,norbornylene, cyclohexene, trans-stilbene, Z-pentene and the like,conjugated dienes and trienes such as pentadiene-1,3,1,2-dihydrobenzene, allo-ocimene, and cyclopentadiene, unconjugateddienes such as mixed octadienes, hexadiene-l,5,2,5-dimethylhexadiene-l,5, 1,4-dihydrobenzene, bicycloheptadiene,bicyclopentadiene, 4-vinylcyclohexene-1, and 4,7-diphenyl decadiene-1,9,acetylenes such as isopropenyl acetylene and phenyl acetylene,chloroolefins such as beta-methallyl chloride and chloromethylnorbornylene, and m-chlorostyrene, ethers and epoxides, esters such asvinyl butyrate, vmyl acetate, and methyl acrylate, and nitrogencompounds such as vinyl carbazole, 4-vinyl pyridine and acrylonitrile,and mixtures and blends thereof.

Products in accordance with the present invention are readily preparedby heat-plastifying a core-forming barrier polymer as hereinbeforedescribed, heat-plastifying a polyolefin material, such as employed inthe outer layers, while in the heat-plastified condition, deforming theheat-plastified polymers to form a layer of polyolefin resin disposedgenerally about the barrier polymer while the polymers are restrainedwithin a configuration, deforming the heat-plastified materials into astream, deforming the stream into a film-like configuration, passing theresultant composite heat-plastified stream into a cooling zone andlowering the temperature of the stream below the heat-plastifyingtemperature thereof.

A wide variety of barrier materials may be employed in the central layerof films in accordance with the present invention. Particularly suitedas barrier layers are combinations of vinylidene-chloride polymers,vinyl-chloride polymers, vinylidene-fluoride polymers and extrudablemixtures thereof. The requirement for the central layer is that thematerial be extrudable within a sheath of another polymer and that thecomposition have the desired gas and moisture vapor transmission barriercharacteristics. Particularly advantageous and beneficial are extrudablecompositions of vinylidene-chloride polymers, wherein the polymerscontain at least about Weight percent vinylidene-chloride, the remainderbeing one or more olefinically unsaturated monomers copolymerizabletherewith. Suitable vinylidene-chloride copolymers are preparedutilizing such comonomers as methyl, ethyl, isobutyl, butyl, octyl and2-ethylhexyl acrylates and methacrylate; phenyl methacrylate, cyclohexylmethacrylate, p-cyclchexylp'henyl methacrylate, chloroethylmethacrylate, 2-nitro-2-imethylpropyl methacrylate, and thecorresponding esters of acrylic acid; methyl alphachloroacrylate, octylalpha-chloroacrylate, methyl isopropenyl ketone, acrylonitrile,methacrylonitrile, methyl vinyl ketone, vinyl chloride, vinyl acetate,vinyl propionate, vinyl chloroacetate, vinyl bromide, styrene, vinylnaphthalene, ethyl vinyl ether, N-vinyl phthalimide, N-vinylsuccinimide, N-vinyl carbazole, isopropenyl acetate, acrylamide,methacrylamide or monoalkyl substitution products thereof, phenyl vinylketone, diethyl fumarate, diethyl maleate, methylene diethyl malonate,dichlorovinylidene fluoride, dimethyl itaconate, diethyl itaconate,dibutyl itaconate, vinyl pyridine, maleic anhydride and allyl glycidylether. Commercially available light stabilizers may also be incorporatedin the vinylidene chloride material such as tertiary-butyl salol. Otherbarrier compositions which may be used with benefit in films inaccordance with the present invention are vinyl chloride polymers whichcontain a predominant amount of vinyl chloride therein, andbeneficially, fluorocarbon polymers, fluorohydrocarbon polymers andfluorohalohydrocarbon polymers may also be used with benefit. Suchmaterials as polyvinyl chloride, polyvinylidene fluoride, chlorinatedpolyethylene and polymers of such materials as vinylidene fluoride,vinylidene fluoride and chlorotrifluoroethylene, chlorotrifluoroethyleneand vinylidene fluoride, chlorotrifluoroethylene and vinyl chloride,chlorotrifluomethylene-vinylidene fluoride and tetrafluoroethylene andthe like. Generally, for economic reasons, the vinylidene chloridepolymers are employed, as they are most readily available at relativelylow cost.

Beneficially, in the extrusion of the vinylidene polymers, it isfrequently advantageous and beneficial to incorporate therein a minorportion of a plasticizer, oftentimes a heat stabilizer and a lightstabilizer. Such additives are well known in the art and generally arefound advantageous in that the temperature required for the extrusion issubstantially reduced and the probability of decomposition of thepolymer in the extruder is lowered. Typical plasticizers which areemployed in the vinylidene or saran combinations are acetyl tributylcitrate, epoxidized soyabean oil (commercially available under the tradedesignation of Paraplex 6-60) and dibutyl sebacate.

Further features and advantages of the present invention will becomemore apparent from the following specification when taken in connectionwith the drawing wherein:

FIG. 1 is an exaggerated isometric view of a packaging film inaccordance with the invention.

FIG. 2 is an exaggerated isometric view of an alternate embodiment ofthe invention.

FIG. 3 is a schematic representation of an apparatus for the preparationof the packaging film of FIGS. 1 and 2 in accordance with the presentinvention.

In FIG. 1, there is illustrated a flexible packaging film generallydesignated by the reference numeral 10. The package 10 comprises a firstouter polyolefin layer 11, a second outer polyolefin layer 12 and acentrally disposed barrier layer 13 consisting of a halocarbon or ahalohydrocarbon. The layers 11, 12 and 13 are securely attached to eachother.

In FIG. 2 is illustrated a view of a packaging film generally designatedby the reference numeral 20. The film comprises a first outer layer 21,a second outer layer 22 of a polyolefin material, a third layer 23 of anoxygen and moisture vapor barrier and bonding layers 24 and 25. Thebonding layers 24 and 25 are of an adhesive material which secures thelayer 21 to the layer 23 and the layer 22 to the layer 23, respectively.

FIG. 3 is a sectional view of an apparatus generally designated by thereference numeral 30, particularly adapted to prepare products such asthe film 10 of FIG. 1 and film 20 of FIG. 2. The apparatus comprises incooperative combination a die or facing body 31 having defined therein afirst elongated passageway 32. The passageway 32 is inoperativecommunication with a source of heat-plastified thermoplastic material33. The direction of flow is indicated by the arrow and the materialidentified by the letter A. The die 31 also defines internal cavities .35 and 36 which are generally commensurate in width with the passageway32. The cavities 35 and 36 are in communication with a heat-plastifiedpolymer source 38 which is so constructed and arranged so as to provideheat-plastified thermoplastic material to the cavities 35 and 36. Theflow material is indicated by the arrow and the type of material isidentified by the letter B. The die 31 defines fourth and fifth internalpassageways 40 and 41 which extend within the die body 31 and aregenerally coextensive in width with the passageway 32. The passageways40 and 41 are in operative communication with a third source 43 of aheat-plastified polyolefin material. The direction of flow is indicatedby the arrow and the material by the letter C. The passageways 32, 40and 41 and the cavities 35 and 36 connect with a common passage 44extending for the width generally commensurate with the passageway 32.The common passageway 44 terminates remote from cavity at the die lips45 and 46 which define an extrusion slot 47.

In the preparation of packaging film of the present invention, a widevarity of extrusion arrangements may be employed. However, forsimplicity, preparation of such films shall be described in accordancewith the extrusion die illustrated in FIG. 3. Employing the arrangementof FIG. 3, one layer, two layer, three, four and five layer films arereadily produced which may be either symmetrical or unsymmetricalwherein the barrier layer is of single or multiple layer construction.If a thermoplastic resinous material is supplied from the source ofthermoplastic resinous material 3.3, 38 or 43, a single layer film willissue from the extrusion orifice 47. Thermoplastic material is suppliedfrom the sources A and B or A and C or B and C. A three-layer film willresult which will have the arrangement of polymer BAB, CAC or CBC.Alternately, a five-layer film is prepared when thermoplastic resinousmaterial is supplied from all three sources. The resultant film has thearrangement of CBABC. If the source B is connected only to the cavity 35and not to the cavity 36, the combination which results is CABC. Whenonly the passageway 40 is connected to the source C, the resultantproduct has the combination of BABC. Beneficially, the proportions orthickness of the various layers are readily controlled within extremelywide limits by the rate of feed from the various polymer sources. Thus,the thicknesses of any of the layers may be varied from essentially amaximum to almost a monomolecular layer by appropriate feed control.Advantageously, in producing a fivelayered film, the barrier material isintroduced from the polymer source A and the hydrocarbon or halogenatedhydrocarbon material introduced from the source C. Beneficially, forcertain instances it is critical to increase the peel strength of theresultant laminate and beneficially the polymer from the source B is anadhesion-promoting material which adheres strongly to the material A andthe material C. Barrier films in accordance with the present inventionbeneficially employ a centrally disposed barrier layer of a high meltingmaterial of low permeability such as saran materials which contain atleast percent vinylidene chloride copolymerized therein and beneficiallypercent and even weight percent. Such saran resins are of a highcrystalline variety and exhi'bit excellent barrier properties. In theextrusion of saran-type resins, it is necessasy to usecorrosion-resistant material until they are separated from theprocessing equipment by a layer of a diverse resinous materialexhibiting lower or lesser corrosive properties. Other barrier materialswhich are eminently satisfactory are hydrocarbons containing fiuorineand chlorine such as polytetrafluo-roethylene,polychlorotrifluoroethylene and copolymers containing major portions ofthe hydrocarbons containing fluorine and chlorine. Polyvinylchloride,polyesters and nylon resins are also satisfactory in many instances asbarrier layers. However, for optimum barrier characteristics, saran andfluorocarbons and fiuorochlorocarbons are generally unsurpassed. Theinterior or central layer of the barrier films shall be such that theoxygen transmission of the total film will be not more than 10 cubiccentimeters per hundred square inches for 24 hours per atmosphere at 70Fahrenheit.

Beneficially, in certain instances, it is desirable to add adhesive orbonding layers between the barrier layer and the outer polyolefin layer.The nature of such bonding or adhesive layers must be such that theadhesion between the outer and inner layer is increased as increasedseal strength and resistance to delamination are to be obtained.

A variety of polymers may be employed for the purpose and coextrudedsimultaneously as the film is formed to provide five-layer film, whereinthe outer layers are of a polyolefin layer, such as polyethylene,polypropylene and the resinous copolymers of ethylene and propylene.

Beneficially, the adhesive layer will vary in thickness from about 0.05to about 0.8 mil; however, generally the preferred range of adhesivelayer thickness is from about 0.1 to about 0.3 mil in thickness.Oftentimes the strength of the bond between the inner or core layer andthe outer or surface layer increases slowly as the thickness of theadhesive layer is increased, and generally little or no increase in thebond strengths occurs after the thickness of the bonding layer hasreached 0.5 to 0.6.

A wide variety of polymers and polymeric compositions are useful toincrease the adhesion between the polyolefin outer layer and the innerbarrier layer. Suitable polymers or polymeric compositions are readilyselected by determining the bonding strength of the composition beingevaluated by forming a two-layer extrusion as is attained when employingthe die of FIG. 3, wherein polymer A is provided and polymer B isprovided to either of the cavities 36 or 35. The bond strength of theresultant two-layer laminate is readily deter-mined by conventional peelstrength tests. Similarly, the adhesive layer composi tion is evaluatedby a similar extrusion utilizing the polyolefin material.

Of great help in selecting the proper adhesive layer material are thesolubility parameters or 6 values. Solubility parameters or 6 values arediscussed in Some Factors Affecting the Solubility of Polymers by P. A.Small, Journal of Applied Chemistry, 3, 71 (1953) and also in SolubilityParameters by Harry Burrell in the Interchemical Review, 14, 3-16, 31-46(1955). For example, some 6 values of typical polymers arepolytetrafluoroethylene 6.2; polypropylene 7.2; polyethylene 7.9;butadiene/ styrene 8.1; polystyrene 9.1; polyethyl acrylate 9.2;chlorinated polyethylene (35 weight percent chlorine) 9.3;polyvinylacetate 9.4; polyvinyl chloride 9.7; 76 percent styrene and 24percent acrylonitrile 10.1; chlorostyrene 10.5; 85 percent vinylidenechloride and 15 percent vinyl chloride 12.2; and polyacrylonitrile 15.4.Generally, adhesion is obtained when a polymer is selected having 6values which are within about 3 units each of the materials to beadhered. For example, polyethylene and the vinylidene chloride polymerare readily adhered by copolymers having 6 values between 9.2 and about10.1. In the instance of adhering layers of polyole-fins such aspolyethylene and polypropylene to vinylidene chloride polymers, polymerswhich are particularly advantageous are copolymers from about 13 weightpercent to about 35 weight percent vinyl acetate with from about 87weight percent to about 65 weight percent ethylene, copolymers of fromabout 20 to 30 weight percent ethylacrylate with from about 80 to 70weight percent ethylene, copolymers from about 20 to 30 weight percentisobutyl acrylate with from about 80 to 70 weight percent of ethylene,chlorinated polyethylene containing from about 25 to 40 weight percentchlorine and polyvinyl chloride.

Beneficial and advantageous thermoplastic resinous films in accordancewith the present invention are employed having thicknesses from aboutone-half to about 20 mils. However, the barrier layer shall have athickness of from about X10 to 4X inches, and the layers shall becombined in the absence of air as within an extrusion die. Beneficially,in many instances, particularly when employing saran compositions, asubstantial and significant increase of the barrier properties isachieved by heat treating the composite film for a period at elevatedtemperatures. Beneficially, such treatment is carried out at atemperature of from about 120 Fahrenheit to about 200 Fahrenheit.Typically, a treating time of 5 minutes at 180 Fahrenheit is verysatisfactory, as the temperature is increased shorter times arerequired, whereas at lower temperatures longer treatment periods aredesirable.

In the preparation of film of the present invention, it is possible toemploy as a central or internal barrier layer materials which are notreadily extruded or shaped into commercially acceptable thin films dueto decomposition or undesirable extrusion characteristics. The provisionof the outer layer of polyolefin material essentially obviates therequirement for close temperature control of the central or inner layeror layers and conditions may vary widely from that generally consideredoptimum for the type of resin employed. Indeed, it is possible toextrude saran resins into smooth transparent composite films which cannot be extruded into such films without the presence of the outer layer.Thus, exceptionally high barrier characteristics can be obtained in afilm which is smooth and transparent, such barrier properties areunavailable in films of equivalent thickness and densities.

Generally, pure polyvinylidene chloride can not be conveniently handledby conventional extrusion techniques. Polyvinylidene chloride decomposesvery rapidly at temperatures which might be expected to permit extrusionthereof. Pure polyvinylidene chloride generally has a molecular weightsufiiciently high that, for practical purposes, it is consideredinfusible, insoluble, and useless for the preparation of thermoplasticresinous articles. However, with the addition of minor portions of othermonomers, a useful thermoplastic extrudable polymer is obtained. Thecharacteristics of such polymers, particularly those which contain about85 weight percent of vinylidenechloride copolymen'zed therein, changerapidly as the weight percentage of vinylidene chloride increases andapproaches 100 percent. -In order to obtain maximum barriercharacteristics both to oxygen and to moisture vapor, it is desirable toinclude within the copolymer as high a weight percentage of vinylidenechloride as is possible with due regard to the tendency of suchmaterials to decompose under heat forming or extrusion conditions. Thus,the use of vinylidene chloride polymers in extrusion or similar heatfabrication operations has been severely limited by the heat stabilitythereof. In order to permit processing of vinylidene chloride polymerscontaining relatively high proportions of vinylidene chloride, it hasbeen necessary to use only copolymers, and these copolymers generallymust contain at least a plasticizer and a heat stabilizer. Oftentimessuch stabilizers and plasticizers comprise two or more components.Generally, in order to provide an extrudable vinylidene chloridecomposition, the nature of the additives which are used is such thatthey are relatively incompatible with the resin system, that is, theheat-fabricated resin or the resin during the heat fabrication has atendency to reject or cause these materials to separate. So, in general,the level of additives to a vinylidene chloride copolymer is maintainedbelow the level of about 10 percent.

Beneficially, the amount of stabilizing additives added to thehalohydrocarbon material, such as the vinylidene chloride composition,can be substantially and significantly reduced below normal levels inthe method of the present invention.

Beneficially, in the embodiments of the invention which utilize anadhesive layer to bond the polyolefin to the halohydrocarbon lightstabilizers which are conventionally utilize'd [in vinylidene chloridecompositions are omitted and a suitable ultraviolet light absorbingstabilizer incorporated in the adhesive composition to provide asufiicient screening of the vinylidene chloride or halohydrocarbon layerfrom ultraviolet light, while avoiding the necessity of incorporatingsignificantly larger amounts of the stabilizer into the central orbarrier layers.

'Much difficulty is encountered in the extrusion and forming of suchcompositions as the stabilizers and plasticizers and various additivestend to separate from the resin frequently at the die face where minutequantities tend to accumulate together with minor portions of materialsuch as the resin itself and a buildup of solid material occurs whichoftentimes will tend to plug or deform the extrusion opening. Such anundesirable situation results in frequent shutdowns to clean theapparatus and in many cases prevents desirably long production runswithout shutdown. This phenomenon of a buildup at the die face underrelatively ideal conditions often results in down time of an extruderranging from 15 minutes to an hour in every 8 hours of operation as wellas considerable waste material. In the extrusion of high vinylidenechloride copolymers, it generally is impractical to stop extrusion ofthe material during cleaning of minor servicing of the extruder, as thepolymer material must be extruded at a temperature that is sufficientlyhigh to cause rapid degradation if the polymer is allowed to remain inthe heated zone of the extruder for a period much greater than theminimal time required to heat plastify the composition and extrude intothe desired form. The matter of decomposition is one of degree. During aheat-forming operation, decomposition of the polymer is continuous and,if extruded rapidly and at optimum temperatures, a commerciallyacceptable product is obtained which shows no apparent decomposition.However, as the residence time of the material in the extruderincreases, black carbon specks and gas voids become apparent and atexcessive residence time the rate of decomposition can become so greatthat the extruder explodes. The decomposition products of vinylidenechloride materials generally include hydrogen chloride, which incombination with a small amount of moisture which is in the feed stockand oftentimes is impractical to eliminate, results in relativelycorrosive conditions existing within the extruder. Therefore, ratherelegant materials such as nickel must be used in the zone of theextruder where the polymer is in a heat-plastified condition. Theextruder barrel, the worm or screw and dies must be extremely resistantto the corrosion. The present invention requires only the necessity ofmaking a relatively small portion of the extrusion equipment corrosionresistant. The screw and the barrel of the polyolefin extruder may beprepared from conventional corrosive susceptible steel and likeconstruction material. 'By encapsulating a flowing stream within apolyolefin layer, the corrosive effect of the vinylidene chloridepolymer is eliminated and the dies employed can be of conventional steelor other desirable materials rather than nickel alloys and the like.Beneficially, the coextrusion technique of the present invention permitsthe use of vinylidene chloride products having much higher barrierproperties than those utilized to make film or sheet from a vinylidenechloride polymer alone. The conditions of extrusion required for thematerial of the outer layer are essentially those which are usable withthe material of the outer layer alone. Thus, for example, in preparing acomposite film in accordance with the invention, the extrusionconditions for the material of the outer layer are those which areoptimum for that outer layer. The temperature conditions required forthe inner layer can vary over relatively wide limits and, in effect,excellent uniform film is obtained when the central layer is extruded attemperatures which would result in rough, opaque and deformed film ifonly material of the central layer were being extruded. Beneficially,extrudable compositions of vinylidene chloride when sandwiched betweentwo or more layers of a diverse polymer will respond favorably to heattreating to increase the resistance to oxygen and moisture vaportransmission. Therefore, in accordance with the present invention,vinylidene chloride polymers having especially low oxygen and moisturevapor transmissions can be handled by extruding and the oxygen andmoisture vapor barrier characteristics can be further improved byheating the resultant compositions at elevated temperatures. The lengthof heating time decreases sharply as the temperature is increased. Thus,films having a relatively low density and high barrier characteristicsare readily prepared using a minimum quantity of vinylidene chloridecopolymer.

Preparation of film in accordance with the present invention hasrelatively high oxygen, carbon dioxide and moisture vapor barriercharacteristics because of the h-alohydrocarbon core. Thehalohydrocarbon resin compositions used in the present invention have ahigher melting point or heat seal temperature than do the polyolefincopolymers suitable for the surface layer. Because of thesecharacteristics, a wide range of temperatures may be employed to heatseal the materials because of the support of the vinylidene chloridebarrier layer. Although the sealing temperatures are above the optimumtemperature for the sealing of a polyolefin film, the halohydrocarbonmaterial at these temperatures still provides adequate mechanicalsupport for the relatively fluid polyolefin layers on the surface. Thepolyolefin surface layer provides excellent abrasion resistance, gloss,clarity and printabili-ty. By employing a generally unoriented ornonbiaxially oriented film, excellent draw characteristics are obtainedas the shrink energy of the films in accordance with the presentinvention is exceptionally low.

By way of further illustration, a plurality of multilayer films wereextruded having the dimensions, compositions and characteristics setforth in the following tables.

TABLE l.EXTRUSION DATA ON 3 & 5 LAYER FILMS Chill Thick- Plastic DieLbs./ roll Sample Layer ness, temp, temp., rate, temp, No. compositionmils C. hr. C.

1 PE D 0.90 190 220 127 is 2 PE (D) 1.80 Saran (A) 0. 40 (D) 1. 80

3 E (B) 1. 85 Saran (A) 0. 30 PE (B) 1. 85

TABLE 1.- Continued Chill 'lhlek- Plastic Die Lbs./ roll Sample Layerness, temp., temp, rate, temp, No. composition mils 0. 0. hr. C

4 PE (B) Saran (A) 40 PE (B) 80 PE (B) PEVAc (C) Saran (A)..- PEVAc (0)PE (B).--

PE (B) PEVAc (C) Saran (A) PE (B) PEVAc (C) Saran (A) PEVAc (0)..... PE(B) PE (B) PEVAc (C) Saran (A) PEVAc (C) PE (B) (13)-. Saran (F).

PE (B) PEVAc (C) Saran (A) PEVAc (C). PE (B) PE (B) PEVAc (0)... Saran(E) PEVAc (0)..... PE B) Saran (H) 10H meta PP 99999 P93 9? P9992" r r'epPpr' H. 99! 9. 9 95 9. 9.

990 poo coo HCQQH HOcOv- P9999 r3099? 9 wh m coo TABLE 1. C ntinuedTABLE 3.-LAYER TO LAYER ADHESION Chili Thick- Plastic Die Lbs./ rollLayer t0 Sample Layer ness, temp., temp., rate, temp., Thicky Peak $6111No. composition mils 0. 0. hr. 0. Layer ness, hesion, strength. SampleNo. composition mils g./in. g./in.

Saran (K) 0. 57 41 PE (B) 0 79 PEVAc (O) Saran (A) 27 PE (B) 0.84 PEVAQL- Saran 0.32 PE PE (B) 0. 85

42 PE B 2s PE (B) 0.13 Z, Saran (L) 0.36 Saran (A) g me (O) 1 B 29 PE(B()MS Saran PE (B (B) Ev.i c) 30 PE (B) 1. 00 PEVAc (C)..... 0.10 55 55Saran (A) 0. so PEVAc (0)... 0.10 PE (B) 1. 00 PE (B) PEVAc (C) 31 PE (B1.53 Saran (A) PEVAc(C) 0.10 PEVAc (C).. Saran (N) 0.20 PE (B PEVAc (C)0.10 PE (B 1. 53 32 PE (B 1.18 PEVAO PEVAc (o). 0.10 Saran (A) Saran (N)0.40 PEVAC PEVAc c 0.10 PE 0 PE (B) 1. 19 PE 0 B 0.9 33 PE 08 PEVAc o).0. PEVAc (O 0.10 Saran (A) 0.40 Sara PEVAc 65"... 0. 40 09 PE (B) 0. 90

95 E (B) 0.80 0. 10 PEVAe (c) 0. 80 Saran (A) 0. 40 10 PEVAc (0) 0. 5095 (B) 0.80

1. 85 0. (B) 1. 20 1.85 PEVAc (8)... 0.10 Saran (A) 0. 40 0.75 PEVAO (S)0.10 0. 50 PE (B) 1.20 0.

38 PE (P) 0.6

Saran (Q)- 0.8 PE (P) 0. 6

39 PE (P) 0.8 Saran (Q). 0. 4 PE (P) 0. 8

c PE (B PVC (R) 1.4 PEVA c (0).. PEVAc (C). 0.1 Saran P]? (O) 1. 2 ggvgSee note at end of Table 3. TABLE 2.PHYSICAL PROPERTIES OF SAMPLES OFTABLE 1 Modulus Tensile Elong. O2 Dart drop, Layer to Heat seal penneft.lbs. layer Sample Percent Gardner, Gloss, C, L, C, C, L, strength,Range, ability, adhesion, o. haze 20? 45 p.s.i. p.s.i. p.s.i. p.5ipercent percent g./in. F. ccJatm. 0 F. 72 F. g./in.

N 0TE.O=cr0sswise to direction of extrusion. L==1engthwise to direction0! extrusion.

PEV Ac (X) Saran (A) .44 PEIBa (Ab)- .28 PE (B) .60

NOTE

(A) 03.75 parts by weight of a copolymer of 85 weight percent viny idenochloride and 15 weight percent vinyl chloride, 4.50 parts by Welghfiacetyltributyl citrate, 1.00 part by weight of an epoxized soyabean 011commercially available under the trade designation of Paraplex G450,0.75 part by weight of 4-tertiarybutyl salol.

(B) Polyethylene, density 0.930, Melt Index 3.8.

(O) Copolymer of 72 weight percent ethylene, 28 weight percent vinylacetate, Melt Index 3.0.

(D) Polyethylene, density .926, Melt Index 20.

(E) (A) plus 2.25 parts by Weight of acetyltributyl citrate. I

(F) 94 parts by weight of a copolymer of 90 weight percent vlnylidcnechloride and 10 weight percent vinyl chloride, 5 weight percent dibutysebacate, 1 weight percent of epoxidized soyabean oil commerciallyavailable under the trade designation Paraplex G-fiO.

(G) 47.5 parts by weight of a copolymer of 85 percent by wei ofvinylidene chloride and 15 parts by weight vinyl chloride, 47.5 par byweight of a copolymer of 73 weight percent of vinylidene chloride and 27weight percent of vinyl chloride, 9 parts by weight dibutyl sebac at ipart by weight of a finely divided magnesium oxide, 5 parts by weight oftitanium dioxide.

(H) A copolymer of 85 weight percent vinylidene chloride and 15 weightpercent vinyl chloride plasticizcd with 3 parts by weight pe hundredparts by weight of copolymer of an epoxidized soyabean Oil commerciallyavailable under the trade designation of Paraplex G 60.

(I) A copolymer of 80 weight percent vinylidene chloride, 10 weightpercent vinyl chloride, 10 weight percent butyl aerylate, with 8 partsby weight per hundred parts of copolyrner of dibutyl sebacate and partby weight based on the Weight of the copolymer of finely dividedmagnesium oxide.

(J) A copolymer of 90 weight percent vinylidene chloride and 10 weightpercent vinyl chloride.

A blend of 00 parts by weight of (A) with 10 parts by weight 0 (L) 93.65parts by weight of a copolymer of 85 weight percent vinylidcne chlorideand weight percent vinyl chloride and mixed with 4.5 parts by weight ofacetyltributyl citrate, 1 part by weight Paraplex G-GO, of a part byweight tertiarybutyl salol, M0 of a part by weight finely dividedtetrasodium pyrophosphate.

(M) 92.5 parts by weight of a copolymer of 85 weight percent vinylidenechloride and 15 weight percent vinyl chloride, 5 parts by weight ofethylphthalylethyl glycolate, 1.5 parts by weight of tertiarybutyl saloland 1 part by weight of Paraplex G-60.

5N2 As (A) but containing only 4 parts by weight of acetyltributyl c1 rae (O) Polypropylene having a melt flow of 16 as determined at 230 C.

(P) A blend of 5 weight percent (0) and 95 weight percent (D).

(Q) A blend of 95 parts by weight (A), 5 parts by weight (0).

(R) Commercially available extrusion grade polyvinyl chloride resin.

(S) A copolymer of 75 weight percent ethylene and weight percent vinylacetate, having a Melt Index or 5.1.

(T) A copolymer of 80 weight percent ethylene and 20 weight percent VAc,having a Melt Index of about 3.0.

(U) A copolymer of 76 weight percent ethylene and 24 weight percentvinyl acetate, having a Melt Index of about 1.8.

(V) A copolymer of 74 percent ethylene and 26 weight percentvinylacetate having a Melt Index of 6.

(W) A mixture of 1 part of B and 3 parts S.

(X) A mixture of 1 part of B and 1 part S.

(Y) Chlorinated polyethylene containing 35 weight percent chlorine 1.3percent crystalline.

(Aa) A copolymer of 70 weight percent ethylene, 30 weight percentethylacrylatc having a Melt Index of about 2.5.

(Ab) A copolymcr of 70 weight percent ethylene and 30 weight percentisobutyl acrylate having a Melt Index of about 2.5.

In a manner similar to the foregoing examples, other beneficial films inaccordance with the invention are prepared by the coextrusion ofpolyethylene as the outer layers of the film (0.55 mil in thickness) andinner layers (0.4 mil in thickness) have the following composition: apolymer of Weight percent vinylidene chloride and 20 weight percentvinyl chloride. When the layers have the preceding dimensionalrelationship in mils, the oxygen transmission of the film is 0.8 cc. perhundred square inches per atmosphere at 70 Fahrenheit. When the barrierlayer of the foregoing film is composed of a copolymcr of 91 weightpercent vinylidcne chloride, 6 weight percent acrylonitrilc, 3 weightpercent methyl methacrylate plus /2 of 1 percent itaconic acid based onthe combined weight of the vinylidenc chloride, acrylonitrile and methylmcthacrylate, the oxygen is 0.6 cc. per hundred square inches peratmosphere at 70 Fahrenheit. When the barrier layer is replaced bypolyvinyl chloride, the oxygen transmission is then 20 cc. per hundredsquare inches per atmosphere at 70 Fahrenheit. Replacement of thebarrier layer by a copolymer of 73 weight percent vinylidene chlorideand 27 weight percent vinyl chloride provides a film having an oxygentransmission of 1.2 cc. per hundred square inches per atmosphere at 70Fahrenheit. When a copolymer of 80 weight percent vinyl chloride and 20Weight percent vinylidene chloride is cmploycd, the oxygen transmissionis 8 cc. per hundred square inches per atmosphere at 70 Fahrenheit. Whenthe barrier layer is replaced by a copolymer of 80 weight percentvinylidene chloride and 20 weight percent vinyl chloridc-acrylonitrile,the oxygen transmission rate is 2 cc. per hundred square inches peratmosphere at 70 Fahrenheit. When the barrier layer is replaced by acopolymer of 80 parts by weight vinylidenc chloride, 14 parts by weightacrylonitrile, 6 parts by weight methyl methacrylate plus /2 part byweight of itaconic acid, the oxygen transmission rate of the film is1.50 cc. per hundred square inches per atmosphere at 70 Fahrenheit. Whenthe barrier layer of the film is replaced by a copolymcr of parts byweight vinylidcne chloride, 9 parts by weight acrylonitrile and 6 partsby weight methyl methacrylatc plus /2 part by weight of itaconic acid,the oxygen transmission of the resultant film is 1.2 cc. per hundredsquare inches per atmosphere at 70 Fahrenheit. When the barrier layer isreplaced with a copolymer of 75 weight percent vinylidenc chloride, 17weight percent acrylonitrile and 8 weight percent methyl methacrylate,the oxygen transmission rate is 1.7 cc. per hundred square inches peratmosphere at 70 Fahrenheit.

Composite film in accordance with the present invention offerssignificant advantages in many packaging applications. For example, filmin accordance with the present invention having an oxygen transmissionrate below about one cubic centimeter per square inches per 24 hours at70 Fahrenheit at one atmosphere of pressure and preferably having atransmission rate below about 1.5 or 1.0 cubic centimeter per 100 squareinches per 24 hours at 70 Fahrenheit under a pressure diifercntial ofone atmosphere is eminently suited for the vacuum packaging of meatproducts. In applications where processed meats are process cured orwholly or partially cooked meat or meat products are being packaged bythe gas packaging technique, the oxygen transmission rate of the filmbeneficially is maintained below about 1.0 cubic centimeters per 100square inches per 24 hours per atmosphere at 70 Fahrenheit. By gaspackaging is meant the technique of enclosing a product within a wrapperor overwrap and removing the oxygen therefrom by means of flushing witha mixture of carbon dioxide and nitrogen or other gas suited to theparticular product being packaged, scaling the package in the desiredatmosphere. Oftentimcs, as such gas packaging techniques result in ahigher pressure within the package than vacuum packaging techniques, thebarrier properties of the film for the gas techniques may not need be asgreat as for vacuum techniques. Frequently, the gas or portions of thegas are absorbed by the product to form a tightly conforming attractivepackage. The barrier characteristics 15 of the film protect the contentsfrom loss of moisture and contact with oxygen.

Beneficially, films in accordance with the invention are employed topackage fresh meat products such as ground beef into what is popularlyknown as a chub" package. (A chub package is a cylindrical packageresembling a sausage wherein a tube of packaging material is closed ateither end of the cylinder in a manner similar to a sausage casing.)

Beneficially, films of the present invention are eminently suited forthe packaging of fresh frozen meat and the vacuum packaging of freshfrozen meat. The films provide a tough abrasion-resistant package whichprovides the necessary barrier properties as well as the crumble orwrinkle resistance, and, because of their abrasion resistance, permitshipping of frozen meats at low temperatures under normal conditionswith substantially little or no failure of the package. Both natural andprocessed cheese and various cheese products are very satisfactorilyprotected by the barrier films of the present invention, both when gaspackaging, vacuum packaging, and simple overwrap procedures areemployed. Other products, such as fresh ground coffee, are preserved forlong periods of time by vacuum packaging or gas packaging within filmsin accordance with the present invention which have an oxygentransmission of less than 2 cc. per 100 square inches per atmosphere at70 Fahrenheit. The toughness and abrasion resistance of the compositefilm as well as the barrier characteristics result in superior low costpackages which are highly attractive. Other desirable and advantageousapplications of the film in accordance with the invention are found inareas where the film is laminated to a supporting material. For example,tobacco pouches are beneficially prepared by laminating to suitablepouch paper film in accordance with the invention. The resultant pouchis readily and easily fabricated from the composite film by heat sealingand provides an inexpensive and especially serviceable pouch whichmaintains the tobacco moist for relatively long periods of time.Further, .such a tobacco pouch, once opened, reclosed and carried aboutin the pocket of a smoker, exhibits excellent wear and flex resistancewhile providing the required barrier properties to maintain the tobaccoin a desired condition for smoking.

Beneficially, composite film in accordance with the present invention isadvantageously laminated with other film and sheet products, such ascoated cellophanes, to provide a packaging material particularly adaptedfor such materials as pharmaceuticals, cosmetics and the like. Thepolyolefin outer layer provides the desired characteristic of heatsealing over a wide range of temperatures and provides excellentchemical resistance. The halohydrocarbon barrier layer providesadditional chemical resistance so such packaging materials are, ingeneral, highly grease resistant, easy to fabricate, abrasion resistantand chemical resistant. A further advantageous laminate is a laminate ofthe film in accordance with the invention to a heat-formable substratehaving relatively high rigidity, such as cellulose triacetate. Smalltwo-part containers are readily formed by first laminating compositefilm of the invention to a substrate of 3 to 5 mil thick cellulosetriacetate, subsequently heat forming to provide a plurality ofcontainer halves wherein the cellulose triacetate layer forms theoutermost layer of the container and subsequently partially sealing thehalves together, filling by techniques well known to the art andsubsequently completely heat sealing the portions together to form aclosed container. Such packages may be formed in a wide variety ofshapes and sizes and are eminently adaptable to powders and liquids,such as soap or surface-active agents, suntan lotions, shampoo, babyoil, hair oil, cough medicine, and the like, particularly where thepackage must retain essential oils, perfumes and the like and exhibitgrease resistance.

Bags and like containers prepared from barrier films in accordance withthe present invention are eminently suited for the gas packaging of nutssuch as peanuts, cashew nuts, walnuts and the like. Such nuts aregenerally packaged in an atmosphere of nitrogen and barrier propertiesof the composite films of the invention which permit the preservation ofthe product over long periods of time without undesired decomposition ofthe oils. The clarity of the film is highly desired in that the productis readily displayed. The film is grease resistant, abrasion resistant,and is readily heat sealed over a wide temperature range to provide anattractive package. Shipment of nuts packaged in film in accordance withthe present invention is especially successful as storage of thepackaged nuts for long periods of time after shipment indicates no lossin the barrier characteristics of the packaging material. Candy and likeconfections are also beneficially protected, particularly hard candywhich tends to be hygroscopic or candy coated with a sugar compositionthat tends to be hygrocscopic. The excellent abrasion resistance of thefilm provides a package of high reliability which may be shipped forlong distances and still retain the attractive bright appearance.

EXAMPLE A About 2000 one-pound packages of natural cheese are preparedemploying a composite film having five layers securely adhered together,the layers comprising a .7 mil layer of polyethylene, a 0.1 mil adhesivelayer consisting of a copolymer of about 28 weight percent vinyl acetateand 72 weight percent polyethylene, a barrier layer 0.4 mil Composition(A), a 0.1 mil layer of the vinyl acetateethylene copolymer and a 0.7mil layer of polyethylene. The packages are prepared on an automaticpackaging machine wherein the film is fed to the machine, blocks ofcheese deposited on the film in spaced relationship to each other, theedges of the film folded upwardly and over the blocks and sealedtogether to form a tube. Air is displaced from the tube by carbondioxide and the tube heat-sealed by means of a bar sealer transverselybetween each block of cheese. The tube is then severed to provide aplurality of generally loosely wrapped onepound blocks of cheese.Heat-sealing temperatures are varied from about 240 Fahrenheit to about290 Fahrenheit and the seals are found to be strong and secure. Theresultant cheese packages are stored at a temperature of about 40-45Fahrenheit for a period of about 16 hours. The carbon dioxide in thepackage is apparently absorbed into the cheese and tight packages areobtained wherein the overwrap conforms to the external configuration ofthe cheese blocks. Cheese packages are packaged into larger shippingcontainers. After 24 hours, the packages are examined and evaluated withregard to the tightness of the overwrap. The overwrap is found in allpackages to conform tightly to the configuration of the cheese blocksindicating no leakage or defective seals. The shipping cartons areclosed, shipped by truck for a distance of 1600 miles and are maintainedat a temperature of about 40 Fahrenheit. The packages on arrival attheir destination are stored in a refrigerated storage area and samplesof the cheese packages removed periodically over a period of six months.The cheese is in excellent condition and salable. Comparative tests withcommercially available overwrap material indicate inferior protection ofthe product by the commercial material.

EXAMPLE B In a manner somewhat similar to Example A, about 1000one-half-pound packages of sliced processed cheese are packaged by meansof conventional commercial packaging equipment in a composite filmconsisting of three layers, the outer layers being low densitypolyethylene having a thickness of 0.65 mil and a central layer of acopolymer of 86 weight percent vinylidene chloride and 14 weight percentvinyl chloride suitably stabilized and plasticized, the thickness of thecentral layer being 1.1 mils. The resultant packages are placed inconventional shipping containers and shipped by refrigerated railroadcar for a distance of about 2600 miles, after which they are unloadedand placed in refrigerated storage at about 40 Fahrenheit. The packagesare periodically removed over a period of about six months and are foundto -'be salable and the contents in an edible condition without sign ofmold or loss of protection. Comparative tests with commerciallyavailable packaging materials indicate inferior performance of thecommercial material.

EXAMPLE C Three hundred 12-ounce packages of liver sausage are preparedutilizing a chub packaging machine and a packaging film in accordancewith the invention comprising a five-layer film wherein the centrallayer, 0.32 mil in thickness) is a copolymer of 85 parts by weightvinylidene chloride and 15 parts by weight vinyl chloride suitablystabilized and plasticized. The outer layers are 0.6 mil thick layers oflow density polyethylene, the intermediate layers between the centraland outer layers are 0.09 mil thick layers of a coploymer of 83 weightpercent ethylene and 17 weight percent vinyl acetate. The generallycylindrical packages are closed by means of a hog ring or acircumferential clamp. The packages of liver sausage are subsequentlyplaced in cartons, each containing 12 packages, and shipped byrefrigerated motor freight for a distance of about 1800 miles, unloaded,and maintained in refrigerated storage for a period of about 28 days.Subsequent examination of the packages indicates all packages to be insalable condition and the contents in an edible condition.

EXAMPLE D In a manner generally similar to Example B, eightouncepackages of sliced hard salami are packaged employing the film employedin Example B. Shipping and storage tests indicate excellent protectionis obtained.

EXAMPLE E Employing apparatus and packaging film of Example C freshground beef is packaged in one-pound and threepound chub packages. Thepackages are subjected to normal merchandising conditions and found tobe eminently satisfactory.

EXAMPLE F A plurality of bags is prepared from a film in accordance withthe invention comprising five layers, the outer layer consisting of 0.5mil thick layers of low density polyethylene, the central layerconsisting of 0.15 mil thick layer of the vinylidene chloride copolymerof Example A and employing intermediate layers 0.07 mil in thickness ofthe ethylene-vinyl acetate copolymer of Example A. The bags are ofsufiicient size to contain one pound of ground roasted coffee beans.Prior to scaling, the bags are flushed with carbon dioxide to removeair. After sealing, the bags of coffee are placed in cartons adapted toreceive 50 bags each and subsequently shipped by motor freight for adistance of about 2800 miles and stored at ambient room temperature fora period of about six weeks. No spoilage of the coffee in the packagesis found and the packages remain clear and transparent withoutexhibiting signs of abrasion by the granular coffee.

EXAMPLE G A film is prepared in accordance with the invention comprisingthree layers, the outer layers each being 0.55 mil thick and the centrallayer consisting of 0.1 mil thick copolyemer of 93 parts vinylidenechloride and 7 parts ethyl acrylate stabilized and plasticized withpercent acetyl tributyl citrate, 1 percent Paraplex G-0 and 0.75 percenttertiarybutyl salol, all percentages being weight percentages based onthe total weight of the vinylidene chloride copolymer. One surface ofthe film is coated with an aqueous dispersion of a copolymer of 60 partsby weight styrene and 40 parts by weight butadiene and the waterremoved. The coated film is then laminated to a sheet of 25-pound pouchpaper between a pair of heated pressure rolls. The resultant paper isfabricated into a plurality of tobacco pouches by heat sealing whereinthe laminated polyethylene-saran-polyethylene film is the inner surfaceof the pouch. About 50 of such pouches are filled with three ounces ofcut pipe tobacco and rolled tightly in the conventional manner. Thefilled pouches are stored at ambient temperature and at a relativehumidity which ranges from about 10 percent to about 40 percent for aperiod of five months. At the end of this period, the tobacco is in amoist and smokeable condition. Several of the pouches are carried bypipe smokers for periods of up to two weeks and no significantdeterioration of the tobacco quality is noted. Several of the pouchesare refilled twice and subjected to use by smokers. The pouches appearin generally good condition with no evidence of failure of the barrierlayer.

EXAMPLE H Five mils cellulose triacetate is laminated to the compositefilm of Example C by means of a styrenebutadiene copolymer adhesive. Theresultant composite film is heat formed by means of vacuum drawing toprovide a plurality of symmetrical container halves, each capable ofcontaining about one fluid ounce. Groups of ten containers are filledwith a commercial detergent solution sold under the trade name of Dovesuntan lotion, baby oil, a liquid cough medicine, cold cream (of thecosmetic variety), and hair oil and subsequently sealed. The containersare stored under ambient conditions for a period of about eight months.On subsequent examination, no significant deterioration of the contentsis observed.

As is apparent from the foregoing specification, the present inventionis susceptible of being embodied with various alterations andmodifications which may differ particularly from those that have beendescribed in the preceding specification and description. For thisreason, it is to be fully understood that all of the foregoing isintended to be merely illustrative and is not to be construed orinterpreted as being restrictive or otherwise limiting of the presentinvention, excepting as it is set forth and defined in thehereto-appended claims.

What is claimed is:

1. A flexible packaging film, the packaging film being scratch resistantand having low shrinkage, the film being an extruded film of coextrudedmaterials and the film comprising (a) a resinous barrier layer havingfirst and second major faces, the barrier layer comprising a copolymerof a major portion of vinylidene chloride and at least one otherolefinically unsaturated monomer,

(b) first and second thermoplastic synthetic resinous bonding layersdisposed on and adhered to the first and second major faces of (a),respectively,

(0) first and second resinous polyolefin layers, the resinous polyolefinbeing a polymer of a-olefin having from 2-8 carbon atoms, the layersdisposed on and adhered to the first and second bonding layers,respectively, the heat sealing temperature of (c) being substantiallyless than (a), the film having an oxygen transmission rate of not morethan 10 cubic centimeters per square inches per 24 hours under oneatmosphere of pressure at 70 F., the layers (a), (b) and (c) beinggenerally unoriented and the resin composition of layer (b) ischemically different from that of layers (a) and (c).

2. The film of claim 1 wherein the oxygen transmission rate is less thanabout 1.5 cubic centimeters per 100 square inches per 24 hours under oneatmosphere of pressure at 70 F.

3. The film of claim 2 wherein (a) contains at least 80 percent byweight vinylidene chloride copolymerized therein.

4. The film of claim 1 wherein (a) has a thickness of from 0.5 to 4mils.

5. The film of claim 1 wherein (b) has a thickness of from 0.05 to 0.8mil.

6. The film of claim 1 wherein the olefin layers are polyethylene.

7. A flexible packaging film, the packaging film being scratch resistantand having low shrinkage, the film being an extruded film of coextrudedmaterials and the film comprising:

(a) a resinous barrier layer having first and second major faces, thebarrier layer comprising a copolymer of at least 80 weight percentvinylidene chloride, the remainder being vinyl chloride;

(b) first and second synthetic resinous bonding layers disposed on andadhered to first and second major faces of (a), the bonding layers beinga copolymer of ethylene and vinyl acetate;

(c) first and second resinous polyethylene layers disposed on andadhered to the first and second bonding layers, respectively, the heatsealing temperature of being substantially less than (a), the filmhaving an oxygen transmission rate of not more than 1.5 cubiccentimeters per 100 square inches per 24 hours under one atmosphere ofpressure at 70 C., each of the layers of (a), (b) and (c) beinggenerally unoriented.

8. The film of claim 1 wherein the film is transparent.

9. The film of claim 1, wherein the barrier layer is a polymer having atleast weight percent vinylidene chloride copolymerized with anotherolefinically unsaturated monomer.

10. The film of claim 1, wherein one of the polyolefin outer surfaces isadhered to a substrate.

11. The film of claim 6 wherein (b) is selected from the groupconsisting of cholrinated polyethylene, a copolymer of ethylene andvinyl acetate, a copolymer of ethylene and isobutyl acrylate, ethyleneand ethylacrylate and polyvinyl chloride.

References Cited UNITED STATES PATENTS 3,219,734 11/1965 Mattin 161-1653,274,004 9/1966 Curler et al. 161--252 2,893,908 7/1959 Antlfinger161242 3,086,216 4/1963 Brooks et a1 161-214 3,152,950 10/1964 Palmquistet a1 161167 3,170,013 2/1965 Ploetz 264-171 3,321,804 5/1967 Breidt eta1 264-171 3,223,761 12/1965 Raley 264171 WILLIAM J. VAN BALEN, PrimaryExaminer US. Cl. X.R.

